The technical scope of this invention is that of processes to install a protective coating on the inner wall of a tube.
The invention relates in particular to gun barrels.
During firing, gun barrels are subjected to heavy thermal and mechanical constraints that lead to premature wear.
Attempts have been made to reduce such wear by depositing a wear-resistant material, such as hard chromium, on the inner surface of the barrel.
To make such a coating an electroplating process is generally used.
This process is costly. It implements voluminous electroplating baths able to receive a gun barrel (4 to 6 m in length) and thus consumes a lot of electrical energy.
Moreover, a coating of chromium electroplating does not have sufficient mechanical strength when modern heavily corrosive ammunition is fired.
Coatings of potentially stronger materials have been made that have a higher melting point (tungsten, molybdenum).
These materials are deposited, for example, by explosion plating or plasma projection.
Patent EP1048921 thus describes a plasma projection process and patent EP1059502 describes an explosion projection process.
Processes implementing explosives are complicated to carry out and cause deformations to the gun barrel.
Plasma projection processes require a machining operation after coating. Moreover, there is no guarantee of obtaining a coating whose structure is homogeneous over the full length of the barrel using such processes.